Multiplicity of stellar systems in the solar neighbourhood, wide binaries, and planet-hosting stars

TL;DR

This thesis provides a comprehensive analysis of stellar multiplicity in the solar neighborhood and its impact on exoplanet systems, expanding known binary populations and revealing correlations between stellar companions and planetary characteristics.

Contribution

It introduces the most complete sample of nearby multiple systems, expands the catalog of wide binaries with Gaia DR3, and explores the influence of stellar companions on exoplanet properties.

Findings

Expanded the sample of wide binaries by over an order of magnitude.

Found that multiple systems host more massive, short-period, and high-eccentricity planets.

Identified significant correlations between stellar companion proximity and planetary eccentricity.

Abstract

This doctoral thesis studies stellar multiplicity in the solar neighborhood (d < 10 pc) and in systems hosting planets (d < 100 pc). Using data from the Washington Double Star Catalogue, Gaia DR3, and a comprehensive literature review, it builds the most complete and homogeneous sample of multiple systems within 10 pc. Multiplicity and companion fractions are derived with reduced uncertainties, providing improved statistical reliability. The analysis of orbital periods from one day to millions of years shows that the log-normal cumulative distribution can be seen as a modern revision of \"Opik's law. A key contribution is the study of wide binaries ({\rho} > 1000 arcsec) with Gaia DR3, expanding the known sample by over an order of magnitude and improving astrometric precision. Newly identified companions, including ultracool dwarfs at the M-L boundary and a hot white dwarf, refine the distinction between true binaries and unrelated young moving-group members. The thesis also explores the effect of multiplicity on exoplanetary systems within 100 pc. New stellar companions are found in known planetary systems, with separations for over 200 pairs and parameters compiled for 276 exoplanets. Compared to single-star systems, multiple systems host more massive, short-period, and high-eccentricity planets. About 22% of exoplanetary systems have stellar companions, with significant (> 4 {\sigma}) correlations between high eccentricities and small projected separations, and a weaker (> 2 {\sigma}) trend showing that massive planets (M > 40 M_Earth) orbit closer in multiple systems. Finally, a review of Giovanni Battista Hodierna's 17th-century catalogues shows he compiled the first list of multiple systems over a century earlier than previously believed, advancing the understanding of stellar multiplicity and its influence on planetary formation.